A device disclosed in Japanese Unexamined Patent Application Publication No. H05-61592A (Patent Document 1) is known as an example of the above-described pressure sensitive sensor and touch panel. In the device disclosed in Patent Document 1, a flexible touch panel 2 is disposed on a planar pressure sensitive sensor 1 to be in contact with the planar pressure sensitive sensor 1 (see FIG. 1 in Patent Document 1). A sensor including a pressure sensitive sheet 1a constituted of a pressure sensitive resistive sheet or the like is given as an example of the pressure sensitive sensor 1, where a pressing force is detected by detecting a change in a resistance value arising when the pressure sensitive sheet 1a is pressed (see paragraph 0015).
However, the resistance value of the pressure sensitive sheet 1a can change not only when actually pressed but also when, for example, the temperature in the vicinity thereof changes. There are thus cases where the effects of ambient temperature cause a drop in the accuracy of detecting the pressing force. Particularly in a structure where a pressure sensitive sensor and a touch panel are combined as in the device disclosed in Patent Document 1, for example, heat is produced by a display device (backlight) such as a liquid crystal display and a controller that handles the execution of various applications, which tends to change the ambient temperature. As a result, it has been difficult to detect an accurate pressing force.